It's definitely an interesting detail.
It seems like King clearly knows the limits of Marco's regeneration BUT wants to tire him out as much as possible until King actually pulls his sword and defeats the heavily weakened Marco.
(That's also interesting for you
@Aknolagon @Ice devil slayer)
It's also note worthy that King hasn't been damaged yet. Why? I think this is already a hint for King's haki specialty - ryuo/barrier haki but King mastered said barrier haki on such a level in which he wears it as an invisible armor almost permanently.
I know, "But G4th timelimit!" - it is not weird that Luffy is literally the only one having this bullshit drawback, even now, when someone like Katakuri literally spammed FUTURE SIGHT 24/7? Dude could perfectly use FS even after 9h with no said drawback of losing haki.
Therefore, only because Luffy has this kind of nerf, doesn't mean King would have the same problem - not to mention that he still wears an invisible armor and not really Haki. Although ryuo itself is more advanced, you're simply flowing your haki outside your body meanwhile you extremely concentrate said flowing part on certain limps to harden them extremely. Thus 'hardening'.
Thus, Marco cannot really injure King because the latter consistently uses barrier haki on himself to stall and weaken Marco even further. Why wasting huge amount of high level attacks if Marco can just regenerate the damage anyway? Therefore the accumulated damage against Marco is important, not the huge ass AP on said attack imo.
Mark my words, black flames King is incoming.
THIS DUO FIGHT WILL BE AMAZING
